In real economy, it is quite familiar that large shareholders expropriate small shareholders' profits. This paper believes that this phenomenan is the inevitable result of the natural unequal power structure between major shareholders and minority shareholders.In this paper, we shart from relaxing the assumption that all shareholders are homogeneous and assuming that there is a natural unequal power structure among the shareholders,and we establish a game model about enterprise surplus distribution to deduce the process of large shareholders expropriating small shareholders' profits and its mechanism. It is pointed out that the realization of interest through control is the inevitable result of market failure, and it can not be solved by market mechanism itself.